This application claims priority of Japanese Application Nos. Hei 11-249480 filed Sept. 3, 1999 and 2000-160033 filed May 30, 1999 and International Application No. PCT/JP00/05818 filed Aug. 29, 2000, the complete disclosure of which are hereby incorporated by reference.
The present invention relates to a wafer holder of a silicon wafer suitable for heat treatment of silicon wafers, and particularly suitable for high temperature anneal treatment in fabricating a SIMOX (Separation by IMplanted OXygen) wafer.
There has been conventionally disclosed a wafer holding apparatus including a plurality of parallelly provided support columns and wafer supporting plates mounted on the support columns, wherein a recessed cut portion is formed in each of the wafer supporting plates where a silicon wafer is loaded (Japanese Patent Application Laid-Open No. HEI-5-114645 (114645/1993)). In this apparatus, the wafer supporting plates are formed of high-melting ceramics such as SiC sintered bodies.
In the thus constructed wafer holding apparatus, wafers are placed on the wafer supporting plates mounted to the columns and are inserted into an electric furnace, so that the contacting areas between the wafer supporting plates and wafers are increased. As a result, loads are not concentrated to a partial area of each wafer, to thereby avoid plastic deformation of wafers upon heat treatment.
Further, forming the recessed cut portion in each wafer supporting plate enables a reduction of the weight of the whole apparatus and allows to move the silicon wafers into and out of the electric furnace such as by pinching the wafers by tweezers.
However, the formation of the recessed cut portion in the wafer supporting plates in the wafer holding apparatus disclosed in the aforementioned Japanese Patent Application Laid-Open No. HEI-5-114645 (114645/1993) brings the supporting plates to be out of point symmetry with respect to the centers of the supporting plates themselves, respectively, so that there is such a possibility that the wafer is warped at the recessed cut portion upon fabricating the supporting plate. Also, there is such a possibility that the silicon wafer is contacted with the edges of the recessed cut portion when the silicon wafer is placed on the wafer supporting plate, to thereby cause crystal defects called xe2x80x9cslipsxe2x80x9d within crystals of the wafer such as due to thermal stresses upon heat treatment.
To overcome this problem, there has been disclosed a vertical semiconductor diffusion furnace aimed jig, in which the jig includes ring-shaped wafer supporting bodies made of silicon carbide substance removably mounted to columns provided between an upper plate and a lower plate (Japanese Patent Application Laid-Open No. HEI-6-163440 (163440/1994)). This jig is constituted to horizontally support peripheries of wafers by the wafer supporting bodies, respectively.
In the thus constituted vertical semiconductor diffusion furnace aimed jig, the wafer supporting bodies are uniformly arranged relative to outer peripheries of wafers and the areas of the wafer supporting bodies are increased, to thereby allow to decrease the unit surface pressure acting on the wafer supporting bodies and to disperse loads thereto. As a result, it becomes possible to avoid occurrence of slips in wafers.
However, in the conventional vertical semiconductor diffusion furnace aimed jig disclosed in the Japanese Patent Application Laid-Open No. HEI-6-163440 (163440/1994), it is difficult to evenly hold wafers at the outer peripheries thereof due to the affection of surface-pendant drops at the outer peripheral portions of wafers when the outer peripheries of wafers contact with the wafer supporting bodies, leading to a possibility of occurrence of slips in wafers.
It is therefore a first object of the present invention to provide a wafer holder capable of restricting occurrence of slips within wafers, by preventing warpage of a holder body upon fabricating the holder body.
It is a second object of the present invention to provide a wafer holder capable of restricting occurrence of slips within wafers, by inhibiting contact of an outer periphery of a wafer with the holder body.
It is a third object of the present invention to provide a wafer holder capable of assuredly holding each of wafers having different diameters without deviating them from pertinent predetermined positions, by the same holder body.
It is a fourth object of the present invention to provide a wafer holder capable of smoothly conducting working operations for loading and unloading the wafer to and from the holder body.
As shown in FIGS. 1 through 3, the invention according to claim 1 is an improvement in a wafer holder comprising a holder body 23 for carrying thereon a wafer 22, the holder body 23 being adapted to be inserted into a plurality of holder-aimed concave recesses 14 formed on supporters 12 accommodated in a heat treatment furnace 10 such that the holder body 23 is held horizontally.
The wafer holder is characterized in: that the holder body 23 is formed into a disk shape free of recessed cut portions; that the holder body 23 is formed with an upwardly projecting ring-like projection 24 extending in the circumferential direction of the holder body 23 around the axis of the holder body 23; that the wafer holder is constituted such that the wafer 22 is to be contacted with the upper surface of the projection 24 and is to be placed on the holder body 23, and that the wafer holder is constituted such that the outer diameter of the projection 24 is formed to be in a range of 0.5D to 0.98D wherein D is a diameter of the wafer 22, and such that the outer periphery of the wafer 22 is kept from contacting with the projection 24.
According to the wafer holder recited in claim 1, the holder body 23 is formed into the disk shape free of recessed cut portions, i.e., the holder body 23 is formed in a point symmetric manner with respect to the axis of the holder body 23, so that no warpage is caused in the holder body 23 even upon fabricating the same. As a result, each wafer 22 evenly contacts with the upper surface of the projection 24 such that substantially no internal stresses are caused within the wafer 22. Further, the outer periphery of the wafer 22 is not contacted with the holder body 23 and it is possible to evenly hold the wafer 22 without the affection of surface-pendant drops of the outer peripheral portion of the wafer 22, so that no slips are caused within the wafer 22.
In the present specification, it is noted here that the term xe2x80x9crecessed cut portionxe2x80x9d means a notch or cutout reaching the vicinity of the center of the holder body, and such a term never embraces those recesses formed at slight depths at the outer periphery of the holder body. In other words, the term xe2x80x9crecessed cut portionxe2x80x9d used in the above never embraces those recesses which are small to such an extent not to cause warpage in the holder body upon fabricating the holder body as used in the present specification.
The invention of claim 2 as shown in FIGS. 1 and 5 is the invention according to claim 1, and is characterized in that the holder body 23 is formed, at the outer periphery thereof, with a convex ring 26 projecting upwardly; that the holder body 23 is formed, inside the convex ring 26, with a plurality of projections 24a, 24b having different diameters, and that the plurality of projections 24a, 24b are formed to be lower than the convex ring 26 and to become sequentially lower from the outermost projection 24a toward inner ones whereas the outermost projection 24a is the highest among them.
According to the wafer holder as recited in claim 2, when the wafer 22 having a larger diameter is placed on the holder body 23, this wafer 22 contacts with the upper surface of the outermost projection 24a, and the horizontal displacement of the outer peripheral surface of the wafer 22 is obstructed by the inner peripheral surface of the convex ring 26. Meanwhile, when the wafer 27 having a smaller diameter is placed on the holder body 23, this wafer 27 contacts with the upper surface of the inside projection 24b, and the horizontal displacement of the outer peripheral surface of the wafer 27 is obstructed by the inner peripheral surface of the outermost projection 24a. As a result, it is possible to assuredly hold each of wafers 22, 27 having different diameters on the same holder body 23 without deviating from a relevant predetermined position.
The invention of claim 3 as shown in FIG. 1 is the invention according to claim 1 or 2, characterized in that the upper surface of the projection 24 is flattened.
According to the wafer holder recited in claim 3, since the upper surface of the projection 24 has been flattened, those bumps caused on the upper surface of the projection 24 such as due to grain growth upon CVD treatment have been removed to thereby smoothen the upper surface of the projection 24. As a result, placing the wafer 22 on the projection 24 causes the wafer 22 to be evenly contacted with the upper surface of the projection 24 such that substantially no internal stresses are caused within the wafer 22, i.e., such that the unit surface pressure of the wafer 22 is reduced and the load of the wafer 22 is dispersed, so that no slips are caused within the wafer 22.
The invention of claim 4 as shown in FIG. 1 is the invention according to claim 3, characterized in that the periphery of the upper surface of the projection 24 is chamfered.
According to the wafer holder recited in claim 4, although the peripheries of the upper surface of the projection 24 become sharp edges when such peripheries are flattened, the sharp edges are removed by chamfering the peripheries of the upper surface of the projection 24 after flattening the upper surface of the projection 24. As a result, no slips due to the peripheries of the upper surface of the projection 24 are caused within the wafer 22 even if the wafer 22 is placed on the projection 24.
The invention of claim 5 as shown in FIG. 4 is the invention according to anyone of claims 1 through 4, characterized in that the holder body 23 is formed, at the center thereof, with a through-hole 23a for allowing insertion therethrough of a plunger 28 for rendering the wafer 22 to be placed on and to depart from the holder body 23.
According to the wafer holder recited in claim 5, loosely inserting the plunger 28 into the through-hole 23a of the holder body 23 from the below of the through-hole 23a to thereby place the wafer 22 onto the upper surface of the plunger 28, and lowering the plunger 28 under this condition, causes the wafer 22 to be placed on the holder body 23 and the plunger 28 to depart from the wafer 22. Reversely to this operation, inserting the plunger 28 into the through-hole 23a of the holder body 23 carrying thereon the wafer 22, from the below of the through-hole 23a, causes the wafer 22 to depart from the holder body 23 and to be placed on the upper surface of the plunger 28. In this way, there can be relatively smoothly conducted the operations for loading and unloading the wafer 22 onto and from the holder body 23.
The invention of claim 6 as shown in FIGS. 6 and 7 is the invention according to anyone of claims 2 through 4, characterized in that the height H of the projection 74 is formed to be 2.0 to 20 mm, that the convex ring 76 is formed, at a portion thereof, with a fork-aimed recess 76a into which a wafer transporting fork 77 is insertable, and that the bottom wall of the fork-aimed recess 76a is formed to lie in the same plane as the holder body 73 around the convex ring 76.
According to the wafer holder recited in claim 6, when the wafer 22 is to be accommodated into the heat treatment furnace, the wafer 22 is firstly placed on each fork 77 and each fork 77 is moved to thereby transport each wafer 22 to the above of each holder body 73, such that each fork 77 is positioned above the fork-aimed recesses 76a of each holder body 73 and such that the center of each wafer 22 coincides with the center of each holder body 73. Next, lowering the fork 77 causes the wafer 22 to contact with the upper surface of the projection 74, and further lowering the fork 77 results in departure of the fork 77 from the wafer 22. Taking the fork 77 out of the fork-aimed recesses 76a under this condition causes each wafer holder 63 carrying thereon each wafer 22 to be accommodated in the heat treatment furnace.
Meanwhile, when each wafer 22 is to be taken out of the heat treatment furnace, each fork 77 is firstly inserted into fork-aimed recesses 76a. Next, raising each fork 77 causes the fork 77 to contact with the lower surface of each wafer 22, and further raising each fork 77 causes each wafer 22 to depart from each projection 74 and to be placed on each fork 77. Each fork 77 is drawn out of the heat treatment furnace under this condition, to thereby take each wafer 22 out of the heat treatment furnace.
The invention of claim 7 as shown in FIGS. 8 and 9 is the invention according to anyone of claims 1 through 4, characterized in that the height H of the projection 94 is formed to be 2.0 to 20 mm, that the convex ring 96 and the projection 94 are formed, at portions of the convex ring 96 and projection 94, respectively, with a plurality of fork-aimed recesses 96a, 93a, 93b into which a wafer transporting fork 97 if insertable, and that the bottom walls of the fork-aimed recesses 96a, 93a, 93b are formed to lie in the same plane as the holder body 93 around the convex ring 96 and the projection 94.
According to the wafer holder recited in claim 7, when the wafer 27 is to be accommodated into the heat treatment furnace, each wafer 27 is firstly placed on each wafer transporting fork 97, and each fork 97 is moved to thereby transport each wafer 27 to the above of each holder body 93 such that the fork 97 is positioned above the forkaimed recesses 96a, 93a, 93b, 98a of the holder body 93 and the center of each wafer 27 coincides with the center of each holder body 93. Next, lowering each fork 97 causes each wafer 27 to contact with the upper surface of each projection 94, and further lowering the fork 97 causes the fork 97 to depart from each wafer 27. Taking each fork 97 out of the fork-aimed recesses 96a, 93a, 93b under this condition causes the wafer holder 83 carrying thereon the wafer 27 to be accommodated in the heat treatment furnace.
Meanwhile, when each wafer 27 is to be taken out of the heat treatment furnace, each fork 97 is firstly inserted into the fork-aimed recesses 96a, 93a, 93b. Next, raising each fork 97 results in contact of this fork 97 with the lower surface of each wafer 27, and further raising the fork 97 causes the wafer 27 to depart from the projection 94 and to be placed on the fork 97. Each fork 97 is drawn out of the heat treatment furnace under this condition to thereby take each wafer 27 out of the heat treatment furnace.
The invention of claim 8 as shown in FIGS. 10 and 11 is the invention according to claim 7, characterized in that both ends of the projection 94 are chamfered.
According to the wafer holder recited in claim 8, although both ends of the fork-aimed recesses 93a, 93b, i.e., both ends of the projection 94 become sharp edges when the upper surface of the projection 94 is flattened, the sharp edges are eliminated by chamfering the both ends of the projection 94 after flattening the upper surface of the projection 94, so that no slips are caused within the wafer 27 even if the wafer 27 is placed on the projection 94.